The present invention relates to a reflection plate having directivity and a display apparatus using the same.
Conventionally, a reflection type display apparatus uses light taken in from external light as illumination light for a display panel and comprises a transmission type display panel 81 such as a liquid crystal display unit or the like which performs display by controlling transmission of light, and a diffusion reflection plate 82 opposed to the back surface of the display panel 81, as shown in FIG. 21.
In this reflection type display apparatus, external light such as natural light or room light entering from the front side of the display panel 81 is reflected by the diffusion reflection plate 82 and reflection light therefrom is used to illuminate the display panel 81 from its back side thereby to perform display. The external light entering from the front side is transmitted through the display panel 81 and is reflected by the diffusion reflection plate 82, as indicated by an arrow in the figure. The light thus diffused within a wide range enters into the display panel 81 from its back surface and is emitted to the front side of the display panel 81.
In general, in order to take in external light mainly from the upper edge of the screen, the reflection type display apparatus of the kind described above is used such that the direction inclined toward the upper edge of the screen (toward the left side in FIG. 21) with respect to the direction vertical to the screen is oriented in the direction from which brighter external light is obtained. The display is viewed from about the front surface direction which is close to the direction vertical to the screen or from about the direction which is inclined toward the lower edge of the screen from the vertical direction.
The conventional reflection type display apparatus using the diffusion reflection plate 82 has a problem that the display is dark. This is because the light reflected by the diffusion reflection plate 82 is widely diffused in directions which do not enter into the display panel 81 and the portion of the reflection light which can be used as illumination light is only the portion of light within a diffusion range within which light enters into the display panel 81. Therefore, the amount of light which enters into the display panel 81 decreases. Further, the. spreading angle of light which is transmitted through the display panel 81 and emitted to the front side is large, so that the brightness of light emitted in the observation angle in which the display is viewed is low.
Display on a display apparatus is normally observed directly from the front side, as described above. In a conventional reflection type display apparatus, the spreading angle of light emitted to the front side of the display panel 81 is large, and only the portion of light emitted directly in the front direction is observed by an observer, and the other portion of the light emitted in oblique directions is not substantially observed by the observer. Therefore, actually observed display is dark as described above.
In case where a mirror reflection plate is used in place of the diffusion reflection plate 82, regular reflection light reflected by the mirror reflection plate is emitted strongly in a specific direction at an angle symmetrical to the incidence angle with respect to the normal line of the reflection plate. However, since the intensity of light emitted in the direction toward the observer of the display panel 81 is weak, display is dark. In addition, since the reflection plate has a mirror structure, the surface distribution of the intensity of the reflection light is not uniform. Further, an environmental background view including the face of the observer and interior illumination devices is reflected on the display.